1. Prior Art
German Patent Application 41 26 107 discusses an acceleration switch, which does not return again to the original position until an acceleration occurs opposite the deflection direction. The German A1 37 37 142 describes a method for manufacturing the switch out of metal with the application of a polymer sacrificial layer. In Microsystems Technologies 90, International Conference on Microelectro, Opto, Mechanical Systems and Components, Berlin, Sep. 10-13, 1990, Springer Publishing House, pp. 529-537, Mohr et al describes the manufacturing of movable structures using the Liga method with the application of a metallic sacrificial layer. Fan et al., IEEE Trans. Electron Dev., vol. 35, pp. 724-730, 1988 describes producing suitable structures for an acceleration switch out of silicon.
2. Summary of the Invention
The object of the present invention is to create an acceleration switch, which has a short reaction time and has a defined switching threshold, and which satisfies stringent safety requirements. This switch should be suited for use in safety devices in motor vehicles.
In accordance with the present invention, the switch opens again by itself when an acceleration threshold is not met in the operative direction.
Since the opening of the switch follows purely on the basis of the mechanical design, no additional control elements are needed which could increase costs or adversely affect safety.
The switching operation is released without being afflicted by friction, and thus by wear. The switching effect according to the invention produces a defined switching threshold and contact force, such that a contact closure characterized by an indefinite transition region between the open and closed circuit state is substantially suppressed. Furthermore, the switch constitutes a simple mechanical system, which is especially rugged and switches quite rapidly due to its small geometric dimensions. The purely mechanical operational principle of the acceleration switch renders it insensitive to electromagnetic disturbances, which can occur, for example in motor vehicles. The switching properties, such as switching threshold, contact force, contact travel and switching time, can be adjusted within broad ranges by the shaping of the springs. The method according to the present invention has the advantage that the acceleration switches are able to be manufactured with a high level of precision. Since the method according to the present invention allows a plurality of acceleration switches to be manufactured concurrently, the manufacturing costs are low.
In accordance with a second embodiment of the present invention, springs are designed quite simply as bending bars, the desired non-linear characteristics being achieved, for example, by a curvature of the springs. By properly dimensioning the springs, the switching threshold and the contact force of the sensor are able to be specified within broad limits by the design. Since the manufacturing costs per switch depend upon the surface area that is consumed, space can be economized and, thus, manufacturing costs can be reduced by arranging the springs in recesses of the seismic mass. When the switch is closed, in accordance with a third embodiment of the present invention, the current flows from the bearing block via the spring and the seismic mass to the contact block. A switch is formed by dividing the contact block, in which case the current can flow from one part of the contact block via the seismic mass to the other part of the contact block. In this refinement of the acceleration switch, the maximum permissible current is not restricted by the geometric dimensions of the springs. By dividing up the seismic mass into a heavy member and a contact bar, one is able to improve the contact closing between the seismic mass and the contact block. The flexible suspension mount of the contact bar ensures that the contact bar contacts both parts of the contact block with nearly the same force. The contact force can be increased by using a lever between the heavy member and the contact bar. In this manner, given a closed acceleration switch, the electrical contact resistance can be reduced to the extent that a large current is able to flow. Thus, the acceleration switch can be used for large-capacity switching, as required, for example, by active passenger-safety systems in motor vehicles. Furthermore, as a result of the elasticity of the lever system, an especially bounce-free switching of the switch is achieved. To use as little surface as possible when the lever proportions are large, it is often beneficial to design the lever as a multi-stage lever. When the lever is likewise suspended on a spring, the contact force is optimized through proper selection of the ratio, given a specified positioning travel of the lever. The contact resistance of the switch is reduced by means of a rare metal coating and knobs. Silicon and metals are particularly suited as materials for manufacturing the switches.
As a result of the method according to the present invention and the design entailing a considerable structure height compared to the spring thickness, a large selectivity is achieved with respect to the direction of the acceleration. It is thus rendered possible for large currents to be switched on a small space.
The bearing block and the contact block are able to be affixed quite simply to an insulating substrate through bonding.